Distillation of oxo alcohols in the presence of intermediate boiling diluents



J. E. MOISE ET AL DISTILLATION OF OXO ALCOHOLS IN Oct. 14, 1952 2,614,071 THE PRESENCE OF INTERMEDIATE BOILING DILUENTS 3 Sheets-Sheet 1 Filed Dec. 29, 1949 M Om 0% On Ow Oh 0 O0 ON O\ cw MQQIbQQMQSMF FOQ D Om r MQDLENMQSMF QOQvS O N am v m m ow\ A UELEWQM 3 MQ3F QM0$ MK r M w 0.8 a M A\ w\ v m.\ Q Q N\ 9 0 0 m m 3 W w 3 AU oowmv 9% o MQDkLQQMQEMF D 7 y 20PEWOQ$OUMQ EUPEQU I 0.3 B .h 0mm Own zoxlh.

JOEKOUJQ Q Patented Get. 14, 1952 DIS TILLATION OF OX0 ALCOHOLS IN THE PRESENCE OF INTERMEDIATE BOILING DILUENTS James E. Moise, Joseph S. Anderson, andFrank B.

Johnson, Baton Rouge, La., assignors to Stand- Company, a corporation ard Oil Development of Delaware Application December 29, 1949, Serial No. 135,784

7 Claims. (Cl. 202-56) This invention relates to an improved method for purifying synthetic alcohols and, more specifically, to a method for purifying higher boiling alcohols derived from the 0x0 process andwhich contain impurities of the type tending to undergo decomposition at the normal atmospheric boiling point of the alcohol.

Co-pending application Serial No. 136,295 describes a method for purifying the synthetic Oxo alcohols by conducting the distillation in amanner such that a significant proportion of the alcohols are left as a bottoms fraction during the alcohol distillation. Co-pending application Serial No. 136,281 utilizes a subatmospheric distillation process for the purification of the synthetic 0x0 alcohols in the prevention of degradation of high boiling impurities.

An improved distillation process for impure alcohols obtained by the. 0x0 process has been discovered. whereby the alcohol i distilled in the presence of an intermediate boiling fraction having a. boiling range of from+20 to 100 degrees Fahrenheit above that of the alcohol, thereby maintaining the liquid temperature below the critical point.

In order to avoid the high bottoms temperatures-which normally exist in a column during distillation of. the 0x0 alcohols, it has been. found advantageous to have present in the distillation zone during the alcohol distillation a material such as an alcohol or hydrocarbon having a somewhat higher boiling range than the alcohol undergoing distillation. This material can be added directly to the alcohol feed to the distillation zone or it can bea higherboiling alcohol formedduring the 0x0 process which is used to produce the alcohol desired. In either case, the efiect on the distillation is to have a bottoms fraction composed largely oithe higher boiling alcohol or hydrocarbon, thus permitting maximum recovery of the desired Oxo alcohol.

. Many alcohols which are of great commercial importance are prepared by synthetic processes and especially by the. so-called Oxo reaction. The term Oxo reaction is a general term used to described the preparation of oxygenated. organic compounds by the reaction of carbon monoxide and hydrogen with olefinic hydrocarsons in the presence of a carbonylation catalyst.

The method is used particularly for the manufacture of various primary alcohols, more specifically octyl alcohols, by operations involving interaction of carbon monoxide, hydrogen, a hydrocarbon mixture containing substantial amounts of heptenes, and a cobalt carbonylation catalyst. vto form octyl aldehydes. and subsequent reduction .hols have previously of these aldehydes by catalytic hydrogenation to a mixture relatively high in alcohols.

Primary alcohols of this general type are of great economic importance and interest because of their use a intermediates in the manufacture of plasticizers of the di-ester type. These alcobeen .supplied mainly by such comparatively costly procedures as aldol condensation of butyraldehyde's, followedby dehydration, and hydrogenation of the. resulting unsaturated octyl aldehyde. The ,Oxo' reaction and subsequent hydrogenation have ,been found tocomprise a highly economicalqand valuable method for manufacturing alcohols-.from-cheap and readily available hydrocarbonv material chiefly of petroleum origin.

In the carbonylation stage of the process, a large number of different types of reaction take place to form a variety of products. The primary reaction products will be aldehydes. These aldehydes themselves can undergo further reactions to yield other products. For instance, the aldehyde condense with each otherto-yield aldols. At least a part of the aldols undergoes dehydration to alpha-beta-unsaturated aldehydes.- Some ketones are also formed under the reaction conditions. A part of the aldehydesformed in.the.reaction zone is hydrogenated to alcoholsv and the alcohols so formed react with 'aldehydes and ketones present to give mixture of acetals, hemiacetals, and ketals. These compounds can undergo further reactions, including dehydration, to give ethers, particularly those of the unsaturated types. The alcohols can esterify the acids presentto give esters. Hydrogenation of apart of the olefin starting feed stock, as well as some deoxygenation of oxygenated intermediates, gives some hydrocarbons in the final Oxo product; In addition, other more complex and less known reactions also occur between the various'intermediates and products obtained thereby yielding a mixture of higher boiling impurities and contaminants of the oxygenated type.

In the hydrogenation'stage, thelmixtures of acids, saturated and unsaturated aldehydes, alcohols, ethers, aldol condensation products, glycols, acetals, ketals and ester 'are hydro qn' ated in the presence of a suitable catalyst to yield more saturated products containing a jhigherpercentage of alcoholsand non-olefinic compounds. Some of these impurities, especially the' unsaturated ethers, acetals,.lzetals, aldols and esters are quite unstable towardheat and are sensitiveigenerallyto high temperature conditions. For instance, in general, the aldols, acetalshemi-acetals and ketals have a 'gre'attendency. to undergo sufficient time.

degradative decomposition reactions whenever the alcohol is subjected to a simple distillation regardless of whether the distillation be carried out at superatmospheric, atmospheric, or subatmospheric pressures provided the critical degradation temperature is reached. In many cases, thermally unstable esters are present and undergo both thermal and hydrolytic decomposition under ordinary distillation conditions.

A mechanism which fits the facts in a general fashion may be formulated in which it is assumed that decomposition reactions of various thermally and hydrolytically unstable materials proceed to an appreciable extent at the distillation temperature of the alcohol being purified, in this particular case, the isooctyl alcohol which has a boiling point of about 193 C. (380 F.) at atmospheric pressure. The decomposition reactions occurring always produce water, especially by aldol dehydration, and this water probably contributes further to decomposition reactions by its hydrolytic action, especially on esters, ketals, acetals, and unsaturated ethers. The more volatile of the decomposition products, including various saturated and unsaturated aldehydes, water, and alcohols (including both isooctyl and other alcohols of lower boiling point), go overhead with the alcohol product and contaminate the latter. Any aldehydes which are, ingeneral, quite volatile, are distilled over with the alcohol fraction in this manner and can subsequently combine 'very readily with the distilled alcohol product,

reforming acetals and hemi-acetals, which are likewise subject to a second decomposition when redistillation of the alcohol fraction is attempted. Furthermore, aldehyde and other decomposition products are objectionable because they lower overall product purity, and, due to instability, cause difficulties in the use of the alcohol. It is believer, however, that this is an oversimplified and incomplete picture of the overall situation;

It can readily be seen that it is diflicult, if not impossible, to obtain relatively complete recovery of the x0 alcohol by a distillation step and at the same time, to avoid contaminating the alcohol product by degradative and thermal decomposition of the higher boiling impurities present in the alcohol. a

Perhaps the most important commercial use for these higher molecular weight alcohols, such as the C8 isooctyl alcohols produced by the 0x0 reaction-is in esterification reactions to. form compounds of the diester type for use as plasti cizers in resin and plastic compositions. Those of the phthalate and adipate type are widely manufactured. Even though an alcohol product .of a synthetic source appears to be colorless, it

frequently contains small amounts of impurities which form colored bodies during the subsequent acid-alcohol reaction. These colored materials are diflicult to remove from the resulting highboiling ester products and result in inferior esters which require additional and excessive purification prior to their use as plasticizers.

Since the alcohols are to be used principally in the preparation of plasticizer esters, the color and general purity qualities are best determined by a study of the ester produced from the alcohol. In typical alcohol esterification operations,

a molal excess of Oxo alcohol is used based on the phthalic anhydride used, that is, about 2.4 moles of alcohol per mole of phthalic anhydride. The esterification reaction is' carried to substantial completion by esterification for a The unreacted alcohol is then stripped off from the ester product preferably under reduced pressure and blended with fresh alcohol for returning to the esterification zone. Thus, undesirable color forming materials have the opportunity to build up during the recycle stages to a point at which they must be purged from the system before continuing the recycling operation. This presents impurity problems when even small amounts of impurities consistently exist in the alcohol.

To obtain the'data on comparative ester Hazen colors, esterification reactions were carried out during a period of 2 hours at the boiling point of the mixture. The crude esterification mixture was then cooled and compared with Hazen color standards. A complete description of the standard Hazen ester color test is found in A. S. T. M. D-268-46.

This same type of problem of unstable impurities also exists in connection with other alcohols made by the 0x0 reaction, and is particularly troublesome for the higher boiling alcohols of the range of C4 to C15 or higher. For example, the C9 alcohols, prepared by the reaction of Ca olefins such as diisobutylene with carbon monoxide and hydrogen may be purified in the same manner as that described herein for the purification of the C8 Oxo alcohols.

It can thus be seen that it is of great desirability to obtain the alcohol products, particularlythose of the type obtainable from synthetic processes of the 0x0 process, as free of aldehydes,

for purification of alcohols containing thermally unstable high boiling impurities obtained from any source, and is especially applicable to treatment of alcohols having from 4 to 15 carbon atoms. It finds particular application in purification of alcohols obtained by the so-c-alled 0x0 reaction mentioned above and especially to alcohols of the CB and C9 class, although the process can also be applied advantageously for other alcohols containing similar types of thermally unstable impurities, particularly alcoholsobtained by hydrogenation of carbonyl compounds.

In the accompanying drawing, Figure 1 is a plot of the analytical distillation of a crude 0x0 alcohol.

Figures 2 and 3 are diagrammatic representations of two different embodiments of our process.

A typical 1C8 crude Oxo alcohol mixture such as can be employed as starting feed in this improved purification process has the follow composition;

Weight per cent Alcohol as C9; 65.0 Aldehyde as Cs 1.8 Acetal as C2-1 3.7 Ester as C9 3.0 Unsaturates as C7 6.3 Acid as Cs 0.1 Water 2.0 saturates and unknowns 18.1

Analytical distillation of the crude Cs 0x0 alcohols from the hydrogenation step following carbonylation of a C7 polymer olefin clearly shows that the impurities exhibit thermal sensitivity in that they appear to decompose at temperatures of about 260 C. (500 F.). Figure 1 shows a plot of data from such an analytical distillation. The vapor and pot temperatureshave been plotted together with an indication of the temperature values at which sample cuts were removed for testing. The plot of the pot temperaature indicates a sharp rise in temperature at about 260" C. (500 F.) showing cracking has begun when about 51% of the'charge has passed overhead.

In Figure 1 in which the batch analytical distillation of a crude Cs Oxo alcohol is plotted, the heavy ends region shows evidence of considerable undesirable cracking. While there does not appear to be any exact critical temperature vfor cracking, since the extent of decomposition" is dependent on the time of high temperature exposure as well as on the temperature, it appears that if a pot or bottoms temperatures of 260 C. (500 F'.) exists for an appreciable time interval, there is extensive decomposition of the heat sensitive bottoms and contamination of the alcohol removed as an overhead stream. The table below shows data obtained in tests carried out on the cuts removed from the analytical distillation.

TABLE.

6 temperature low, such that cracking of bottoms impurities and subsequent alcohol contamination are virtually prevented.

For instance, in distilling a crude Cs 0x0 alcohol boiling in a range of 175-193 C. (350-380 F.) it is convenient to add a thermally stable, inert material of boiling range 205-260" C. (100-500 F). This material can be a high boiling alcohol, as a Ca 0x0 alcohol, boiling about 205 C. (400 F.) if available. Hydrocarbon fractions of the proper boiling range are also. conveniently. useful. For example, an inert fraction boilingbetween 205-250" C. (400-500" F.) can be employed in conjunction with a Ce alcohol. For other alcohols, the materials to be added are chosen with boiling points and ranges suitably adjusted. The hydrocarbon can be recovered and recycled to the distillation. Care should be exercised in -'ChOSing the inert fraction to avoid one which formsan azeotrope or constant boiling mixture with the alcohol being recovered.

It is also an additional feature that, rather than add an inert hydrocarbon material to the distillation, the olefinic feed to the Oxo reaction itself should be a mixture containing a portion "of an olefin for which the corresponding alcohol derived by the Oxo reaction, will have a boiling point in the range required to prevent high bottoms temperature. This higher molecular weight alcohol can be recovered later and recycled or used otherwise.

Cut s 7 s 9 i0 i1 12 13 14 Ultraviolet Absorption at 25005.. 2.000 1.475 0. M2 0. 191 0. 230 0.210 0. 316 0. 955 1. 800 Alcohol Hazen N o 50 180 25 25 25 150 150 Phthalation Ester Hazen N0 220 520 240 120 195 220 320 460 500 (Pt-Co Scale) Since ester color is considered to be extremely critical and is perhaps the most important quality factor in determining the usefulness of the 0x0 alcohols to prepare the ester plasticizers, the above data in the table are very important in that they clearly show that certain of distilled cuts of Oxo alcohol are clearly superior to other cuts for preparing such esters. Thus, the cuts numbered 8 to 11 are superior as to this very critical quality to cuts 12 to 14, the latter bein obtained, as shown in the graph of Figure 1, after the pot temperature had risen to and above the critical decomposition point of 260 C. (500 F.), the temperature at which the higher boiling OX0 alcohol impurities start to undergo thermal cracking and degradation as is shown by the high ester Hazen number in the above table for these cuts.

In order to avoid the difiiculties of either losin a substantial portion of the alcohol in the bottom by stopping the distillation below the temperature at which cracking takes place, or recovering the major portion of alcohol in an impure state contaminated by color forming impurities produced by the cracking of the bottoms, it has been found highly effective to add an additional agent to the alcohol undergoing distillation.

A liquid of boiling point about 20 to 100 degrees on the Fahrenheit scale above the, boiling.

and, at the same time, assists in keeping the In either case, the effect on the distillation is to have a bottoms fraction composed largely-of the added alcohol or hydrocarbon, thus permitting maximum recovery of the desired Oxo alcohol. To this end the amount of the higher boiling material used is not critical but should be sufiicient to effectively maintain lower temperatures in the iractionating tower bottoms. An amount of from 10% to 50% based on the total feed is adequate for temperature control. For economy purposes, the amount used should be that which is low enough to do the proper job effectively.

It is considered that the improvements obtained by the use of this higher boiling material may be achieved by applying this process in any type of operation wherein an Oxo alcohol or al- 'cohol containing high boiling impurities sensitive to thermal decomposition is subjected to a distillation.

Two specific embodiments of this improved process are presented herewith although it is to be understood that the invention may be practiced in other ways which will be apparent to those skilled in the art.

Example 1 This example can best be understood by read ing it in conjunction with Figure 2. About'9 parts by volume of a mixed olefin feed containing approximately C7 olefin and 20% Cs olefin is fed by line I to an Oxo alcohol plant 2 wherein the .olefins undergo carbonylation by catalytic reaction with carbon monoxide and hydrogen under suitable conditions of temperature and pressure, to give aldehydes, followed by a catalytic hydrogenation of the aldehydes to a mixture of about 100 parts by volume of Ca and C9 Oxo alcohols together with higher boiling impurities such as ethers, esters, and acetals. About 100 parts by volume of these mixed alcohols are passed via line 3 to an intermediate point of topping tower 4. From overhead of tower 4 by line 5 a vapor stream is obtained which is liquefied'in condenser 6 and obtained in line 1 as a recovered stream of about 20 parts by volume of unreacted olefinic feed. From the bottom of topping tower 4, the alcohols and higher boiling impurities are removed through line H. A part of the alcohol stream in line H is recycled back to the tower by lines 8 and I and through external heater 9 to supply heat for the tower. About 80 parts by volume of the feed is eventually removed as mixed C8 and C9 alcohols and higher boiling impurities by line I I and passed to an intermediate point of alcohol distillation tower [2. Overhead from distillation tower 12, there is removed a Ca alcohol fraction by line 13. This alcohol is condensed in condenser 14 and a liquid stream removed by line 15. A part of this stream is recycled back to the distillation tower l2 by line [1 as reflux and a portion, about 48 parts by volume of the 80 parts of feed to tower I 2, is recovered as finished Cs Oxo alcohol of boiling point 175-193 C. (350-380 F.). This Ca alcohol fraction is relatively free of color forming impurities because of the presence of the C9 alcohol in the bottoms product. This Cg fraction permits the temperature operation of distillation tower l2 to be kept lower. Thus, the bottoms temperature does not substantially exceed 260 0. (500 F.), and at the same time recovery of Ca alcohol is substantially complete. From the lower part of the tower 12 by line 2| a stream of C9 alcohol and bottoms is removed. A part of this stream is recycled by lines I8 and 20 through outside heater 19 to the tower l2 to supply heat. The remainder of the mixture is passed through line 2| to a C9 alcohol recovery tower 22. Overhead from tower 22 there is removed a vapor stream of C9 alcohol which is passed to a condensing and treating system 24 from which it emerges through line 25 as about 12 parts of finished C9 alcohol of boiling range 193-2l0 C. (380-410 F.).

From the lower part of recovery tower 22 in which the bottoms temperature is 260 C. (500 F.) or higher, there is removed via line 26, a bottoms product, a major portion of which boils over 210 C. (410 F.). A part of this higher boiling material consisting of acetals, ethers, and esters, is recycled by lines 21 and 29, through external heater 28, back to tower 22 and about 20 parts by volume is removed as bottoms by line 30.

Example 2 As an alternate procedure in which a suitably boiling hydrocarbon fraction is added to the alcohol, Example 2 is best understood by reference to Figure 3.

About 90 parts by volume of a relatively pure C7 olefin is fed by line 50 to an Oxo alcohol plane wherein the olefin undergoes carbonylation by a catalytic reaction with carbon monoxide and hydrogen under suitable conditions of temperature and pressure to give a Ca aldehyde, followed by a catalytic hydrogenation of the aldehyde to about 100 parts by volume of an isooctyl alcohol together with higher boiling tower 62 to supply heat.

impurities such as ethers, esters, and acetals. About parts by volume of this Ca alcohol is passed by line 52 into an intermediate point of topping tower 53. From overhead of tower 53 by line 54 a vapor stream is obtained which is liquefied in condenser 55 and obtained in line 56 as a recovered stream of about 20 parts of unreacted olefinic feed. From the bottom of topping tower 53 th alcohol and higher boiling impurities are removed through line 51. A part of this stream is recycled via lines 58 and 60 through external heater 59 back to tower 53 to supply heat thereto. A major portion consisting of about 80 parts by volume of the impure alcohol stream is taken by line 61 to an intermediate point of alcohol distillation tower 62. There is introduced into line 6| and subsequently into the tower 62 at least 10 parts by volume of a stable hydrocarbon cut boiling from 205- 260 C. MOO-500 F.). The hydrocarbon cut may be from a recycle stream or it may be fresh make-up feed. Overhead from distillation tower 62, there is removed a C3 alcohol vapor stream by line 63. This vapor stream is condensed by condenser 64 and a liquid alcohol stream is collected in line 66 a portion of which is refluxed back to tower 62 by line 61. About 60 parts by volume of finished Cs alcohol of boiling range -193 C. (350-380 F.), from the 80 parts of impure alcohol, are recovered from tower 62. This Cs alcohol fraction is relatively free of color forming impurities because of the presence of the stable hydrocarbon fraction in the tower bottoms. This hydrocarbon fraction permits the temperature operation of distillation tower 62 to be kept lower. Thus, the bottoms temperatures does not substantially exceed 232 C. (450 F.) or, at a maximum 260 C. (500 F.), and, at the same time, recovery of the Ca alcohol is substantially complete. From the lower part of the tower 62 by line 68 a stream of hydrocarbon and high boiling bottoms is removed. A part of this stream is recycled by lines 69 and 1| through outside heater 10 to the The remainder of the high boiling mixture is passed through line 68 to a hydrocarbon recovery tower 12. Overhead from tower 12 there is removed a vapor stream of the hydrocarbon out which is passed to a condensing and treating system 14 from which the recovered hydrocarbon cut is passed by lines 15, 82, and GI back to alcohol distillation tower 62. Through hydrocarbon make-up line 8l'additional hydrocarbon is added if necessary to supply the proper amount of hydrocarbon cut to tower 62 to keep the bottoms temperature below 232-260 C. (450-500 F.).

From the lower part of hydrocarbon recovery tower 12 in which the bottoms temperature is 500 F. or higher, there is removed via line 16 a high boiling bottoms product, the major portion being acetals, ethers, and esters. A part of this is recycled by lines 11 and 19 through heater 18 back to tower 12. About 20 parts are removed as bottoms byline 80.

What is claimed is:

1. An improved distillation process forthe purification of an impure primary alcohol produced by the 0x0 process and containing from four to fifteen carbon atoms and which contains high boiling unstable impurities including acetals, esters, hemi-acetals and ethers which tend to decompose upon heating, which comprises subjecting the alcohol to a vaporization in a vaporization zone in the presence of an inert,

thermally stable liquid, which does not azeotrope with and has a boiling point of from 20 to 100 Fahrenheit degrees above that of the alcohol, the boiling point of said inert liquid being intermediate to the alcohol being purified and the high boiling impurities, maintaining the liquid temperature in the vaporization zone at all times below the critical decomposition temperature of the high boiling unstable impurities, said critical decomposition temperature being higher than normal boiling point of the alcohol being purified, and recovering as a vapor stream substantially all of the alcohol uncontaminated by volatile impurities.

A process such as that described in claim 1 in which the inert, thermally stable liquid is present in an amount of from to 50% based on the total liquid including the alcohol.

3. An improved continuous distillation process for the urification of a primary alcohol having from i to carbon atoms containing high boiling unstable impurities including acetals, esters, hemi-acetals and others and obtained by the catalytic reaction of olefins with carbon monoxide and hydrogen and subsequent hydrogenation of the aldehydes resulting therefrom, which comprises introducing said alcohol and impur= ities together with an inert, thermally stable alcohol higher boiling than the alcohol being purified, said higher boiling alcohol being one which does not azeotrope with and has a boiling point of from to 100 Fahrenheit degrees above that or the alcohol being purified into a distillation cone, the boiling point of said inert alcohol being intermediate to the alcohol being purified and the high boiling impurities, continuously maintaining the liquid within said zone below the critical decomposition temperature of the high boiling unstable impurities said critical decomposition temperature being higher than normal boiling point of the alcohol being purified, recovering as a vapor stream substantially all of the alcohol being purified uncontaminated by volatile impurities, and recovering the inert, thermally stable higher boiling alcohol as a separate fraction.

4. A process such as that described in claim 3 in which the inert thermally stable higher boiling alcohol is present in an amount of from 10% to 50% based on the total liquid including the alcohol being purified.

5. An improved continuous distillation process for the purification of a primary Cs isooctyl alcohol of normal boiling range 350 to 380 F., obtained by catalytic reaction of a C7 olefin stream with carbon monoxide and hydrogen and subsequent hydrogenation of the C8 aldehydes obtained therefrom, and containing high boiling thermally unstable impurities including acetals, esters, hemi-acetals and ethers, which comprises introducing said alcohol and impurities, together with an inert, thermally stable alcohol higher boiling than the alcohol being purified, said higher boiling alcohol being one which does not aseotrope with the Ca iso-octyl alcohol and has a boiling point of from 400 to 500 F., into a dis tillation zone, the boiling point of said inert alcohol being intermediate to the alcohol being purified and the high boiling impurities, continuously maintaining the liquid within said zonebelow 500 F., removing overhead as a vapor stream from said distillation zone substantially all the C3 isooctyl alcohol uncontaminated by volatile impurities, and recovering the inert, thermally stable higher boiling alcohol as a sep-- arate fraction.

6. A process as described in claim 5 in which the inert thermally stable liquid is a hydrocarbon iraction of 400 to 500 F., boiling range and in which the hydrocarbon is separated from the high boiling bottoms of the distillation zoneand recycled back to the distillation zone.

'7. An improved continuous distillation process for the purification of an impure primary Ce isooctyl alcohol of boiling range 350380 F. obtained by the catalytic reaction of olefins with carbon monoxide and hydrogen and subsequent hydrogenation of the aldehydes resulting therefrom, which comprises reacting a mixed olefin stream containing substantial proportions of C-z and Cs olefins with carbon monoxide and hy drogen, subsequently hydrogenating the Ca and C9 aldehydes obtained therefrom, introducing the resulting Cs and Ca alcohol mixture together with high boiling, thermally unstable impurities including acetals, esters, hemi-acetals and others into a distillation zone, the boiling point or" said C9 alcohol being intermediate to the C8 alcohol and the high boiling impurities, maintaining continuous reflux within said distillation zone, maintaining the temperature within said distillation zone at all times below 500 F, removing overhead from said distillation zone as a vapor stream substantially all the Ca alcohol uncon taminated by volatile impurities, removing as liquid bottoms from said distillation zone a mixture of C9 alcohol and high-boiling impurities including acetals, esters, hemi-acetals and others, introducing said bottoms mixture into a second distillation zone, removing overhead from said second distillation zone substantially all the C9 alcohol, and removing from the lower portion of said second distillation zone the high-boiling, thermally unstable impurities as a liquid bottoms product.

JAMES E. MOISE. JOSEPH S. ANDERSON. FRANK B. JOHNSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,835,571 Morley Dec. 8, 1931 2,411,346 Teter et al. Nov. 18, 1946 2,417,886 Redcay Mar. 25, 1947 2,442,229 Berg May 25, 1948 

1. AN IMPROVED DISTILLATION PROCESS FOR THE PURIFICATION OF AN IMPURE PRIMARY ALCOHOL PRODUCED BY THE OXO PROCESS AND CONTAINING FROM FOUR TO FIFTEEN CARBON ATOMS AND WHICH CONTAINS HIGH BOILING UNSTABLE IMPURITIES INCLUDING ACETALS, ESTERS, HEMI-ACETALS AND ETHERS WHICH TEND TO DECOMPOSE UPON HEATING, WHICH COMPRISES SUBJECTING THE ALCOHOL TO A VAPORIZATION IN A VAPORIZATION ZONE IN THE PRESENCE OF AN INERT. THERMALLY STABLE LIQUID, WHICH DOES NOT AZEOTROPE WITH AND HAS A BOILING POINT OF FROM 20 TO 100 FAHRENHEIT DEGREES ABOVE THAT OF THE ALCOHOL, THE BOILING POINT OF SAID INERT LIQUID BEING INTERMEDIATE TO THE ALCOHOL BEING PURIFIED AND THE HIGH BOILING IMPURITIES, MAINTAINING THE LIQUID TEMPERATURE IN THE VAPORIZATION ZONE AT ALL TIMES BELOW THE CRITICAL DECOMPOSITION TEMPERATURE OF THE HIGH BOILING UNSTABLE IMPURITIES SAID CRITICAL DECOMPOSITION TEMPERATURE BEING HIGHER THAN NORMAL BOILING POINT OF THE ALCOHOL BEING PURIFIED, AND RECOVERING AS A VAPOR STREAM SUBSTANTIALLY ALL OF THE ALCOHOL UNCONTAMINATED BY VOLATILE IMPURITIES. 